1. Field of the Invention
The present invention relates to a method for controlling cooking by using a vapor sensor in a microwave oven, and more particularly to a method for controlling cooking by using a vapor sensor in a microwave oven, in which a malfunction of the vapor sensor caused by different sizes of containers filled with food subjected to heating is prevented while food is cooked by means of me microwave oven equipped with the vapor sensor therein.
2. Description of the Prior Art
FIG. 1 is a schematic construction view for showing an internal structure of general microwave oven equipped with a vapor sensor therein. As shown in FIG. 1, in microwave oven 10 for controlling an automatic cooking operation by using the vapor sensor, while a high voltage transformer 100 applies a high voltage electricity to a magnetron 200, microwave is generated from the magnetron 200, and the microwave heats food within a cooking chamber formed by a cavity 300.
Meanwhile, water vapor is generated from the heated food, and then discharged along the air flow which effuse from first blow holes 311 formed in the upper portion of a first sidewall 310 of cavity 300 by a blow operation of a fan motor 400 and sequentially passes through first exhaust holes 321 formed in the lower portion of a second sidewall 320 disposed in opposition to first sidewall 310 and first discharge holes 500. Also, the water vapor is discharged along the air flow which sequentially passes through second exhaust holes 331 formed in the central portion of a ceiling portion 130 of cavity 300, a wind path 500 and second discharge holes 700. Then, the energy of the water vapor discharged along wind path 500 is sensed by vapor sensor 800 which also has the characteristics of a piezo-electric device attached to inlets of second discharge holes 700, so that a heating time is properly adjusted to control the automatic cooking operation.
When vapor sensor 800 sucks in or discharges heat, vapor sensor 800 outputs a detecting signal in the form of an alternating current signal. The magnitudes of the detecting signals at 0.degree. C. and 100.degree. C. are respectively very small positive values which are similar to each other. As another example, if the temperature increases from 0.degree. C. to 100.degree. C., then the value of the detecting signal increases in a positive (+) direction. On the contrary, if the temperature decreases from 100.degree. C. to 90.degree. C., then the value of the detecting signal decreases in a negative (-) direction.
In an automatic cooking mode in which vapor sensor 800 is used, the output of magnetron 200 is similarly applied regardless of the amount of food subjected to heating, the size, or the shape of the container filled with food subjected to heating. Therefore, if the amount of food subjected to heating increases with respect to the same container, the time interval until cooking completion lengthens but the output of vapor sensor 800 becomes similar. However, if the size of the container increases with respect to the same amount of food subjected to heating, the time interval until cooking completion shortens and the output of vapor sensor 800 decreases.
One example of an automatic thawing device of a microwave oven and control method thereof is disclosed in U.S. Pat. No. 5,436,433 issued to Kim et al. Here, a turntable is rotatably placed in a cooking chamber. A gas sensor is placed about an exhaust port of the oven and senses the amount of gas or vapor exhausted from the cooking chamber through the exhaust port during a thawing operation, and outputs a gas amount signal to a microprocessor. The microprocessor calculates the thawing time by an operation of the output signal of the gas sensor and outputs a thawing control signal for driving the microwave oven. An output drive means controls output level of electromagnetic wave of high frequency of a magnetron in accordance with the thawing control signal of the microprocessor. The magnetron generates the electromagnetic wave of high frequency in accordance with the output signal of the drive means for the thawing time. A power source supplies an electric power to the thawing device in accordance with the thawing control signal of the microprocessor.
U.S. Pat. No. 5,445,009 issued to Yang et al. is given as an example of an apparatus and method for detecting humidity in a microwave oven. The apparatus and method for removing the influence of microwave noise without any shielding parts increases the reliability of detected humidity information. According to this patent, the cumulative difference of humidity values sensed by a humidity sensor is calculated for each half period of a commercial alternating current frequence, oscillating and non-oscillating terms of a magnetron are determined by comparing the calculated cumulative differences with each other, and the humidity-sensed values obtained during the determined non-oscillating terms of the magnetron are used as humidity information for automatic cooking control. In order to even further remove the influence of the microwave noise, the humidity sensor may include capacitors for bypassing the microwave noise introduced into the sensor.
As on example of a method for automatically controlling the cooking of food with a low moisture content, U.S. Pat. No. 5,395,633 issued to Lee et al. discloses an automatic cooking control method capable of cooking food with a low moisture content at an optimum by utilizing a variation in an output voltage of a humidity sensor. When a key signal corresponding to food with the low moisture content is received, an initialization is performed. Then, the maximum voltage indicative of the maximum humidity is determined by reading the continuously increasing output voltage from the humidity sensor 10 times for 10 seconds. After the determination of the maximum voltage, a determination is made whether the output voltage has reached a sensing voltage corresponding to a voltage obtained by deducing, from the maximum voltage, a mixture voltage varied depending on the kind of food. The cooking operation is complexed when the output voltage from the humidity sensor has reached the sensing voltage.
Hence, when the same amount of food is served in the containers having different sizes and then heated in the conventional microwave oven which controls the automatic cooking operation by using the vapor sensor, a different cooking result is produced in accordance with the size of the container. However, as a user anticipates the same cooking result with respect to the same food subjected to heating regardless of the size of the container, the user misunderstands the performance of the microwave oven, thereby reducing the user's reliability concerning the performance of the microwave oven and the consumer's intention with which the microwave oven is purchased.